Modern word processing equipment and especially printers for word processing machines, computer terminals and the like may comprise a so-called print wheel which is constituted by a disk having a hub removably mounted upon the machine and formed with a flexible perimeter provided with a font of typefaces or characters which represent characters programmed in the electronic circuitry of the machine and are adapted to be reproduced upon a paper moved past a platen by a hammer or like member positioned to strike a flexible portion of the wheel, drive the typeface against a pigment carrier such as a ribbon, and thereby reproduce an image of the typeface on the paper.
The flexible perimeter of the wheel may be formed by providing the wheel as a so-called daisy wheel, i.e. forming each typeface upon a respective radial arm or spoke extending outwardly from the hub and thus resiliently displaceable out of the plane of the wheel or disk by the hammer upon impact to print the respective character.
Such wheels may be composed of metal or of a resilient synthetic resin material and generally have a limited life but, because they are of low cost and weight, are able to provide rapid high quality printing in an economical and convenient manner.
As noted, such wheels are conveniently utilized together with a ribbon, band or strip carrying the pigment, e.g. a so-called carbon ribbon, which may be disposable, or even a ribbon which may be reinked after each passage across the wheel. The ribbon can be carried on spools or a cartridge or cassette.
While print wheels of the aforedescribed type have been found to be highly effective in high speed typewriting and print output, especially in association with cassette ribbons, the operating cost of conventional equipment utilizing such print wheels is found to be comparatively high because of the frequent need to replace the ribbon reels. Cassettes have an advantage over reel-type ribbons since they can contain the reinking supply in such manner that replacement of the ribbon is possible, together with the reinking supply as a unit, without soiling the hands of the operator. However, the cassettes themselves are fairly complex, expensive to manufacture and, therefore, expensive to replace.
The print wheels, whether composed of synthetic resin material or metal, must be replaced upon rupture of one of the spokes or damage to or wear of a typeface. Generally speaking such wheels can be readily removed from the machine by the operator and replaced by another wheel kept on hand for this purpose.